it was kept here until the 1st world war when it was sent to the united states to keep it safe. some art experts are skeptical mona lisa has a twin. they argue it's more likely an anonymous painter who was trying to copy da vinci. >> i've seen the infrareds and the x-rays. they are not characteristic of what leonardo does in these paintings. >> reporter: about 6 million people visit the louvre in paris each year to see the mona lisa. museum officials would not comment on claims of a second portrait. the debate will likely linger. the swiss foundation says it will not sell the painting or reveal who currently owns it. >> the mystery goes on. historians with the mona lisa foundation believe da vinci painted the earlier portrait 10 to 12 years before the original mona lisa. >> another quick look outside where things are booming and turbulent. >> let's start with the watch that covers the entire metro area until midnight, the severe thunderstorm watch. the deeper yellow is a warning in loudoun county, prince william county, fauquier county and a little sliver of montgomery county. w